The Wall Brown is a widespread but now less common species of short open grassland with patches of bare ground such as coastal cliffs, dunes, disturbed land (such as old quarries and railway land), grassy farm tracks and some arable field margins. The caterpillars feed on various grasses. The decline of this species has been particularly severe inland with extinctions occurring at many sites in central southern England. (For further details on this species see http://www.butterfly-conservation.org/).

Status details : Status since 1976 is Rapid decline with a decrease of -89.1%Status over the last 20 years is Rapid decline with a decrease of -78.2%Status over the last 10 years is Stable with a decrease of -41.8%

Log collated index plot

This chart shows the index of abundance (LCI = Log Collated Index) over time. It shows fluctuations in
populations from year to year, and is scaled so that the average index over the whole series is equal to 2
(horizontal line). For greater detail about how this index is derived, click on the green question mark above.

Trend description :The Wall Brown shows very large cyclic fluctuations in abundance, suggesting an interaction with parasitoids. The first generation indices show no significant trend, but numbers recorded in the first generation are often very low. The second generation indices however show a significant decline. At the site level the vast majority of sites show declines and at many sites (mostly inland sites) the species is either extinct or close to extinction. The only site showing a substantial increase in numbers is Gibraltar Point on the Lincolnshire coast. No satisfactory explanation has so far been put forward to explain the decline of this species which has particularly affected the species in inland southern England. Currently most sites with higher counts are either coastal or northern sites.

Phenology plot

Phenology plot

This chart shows the average number of butterflies seen on transects between Arpil and October across all sites (fitted values from a Generalised Additive Model). The blue line gives average counts over the full BMS series (1976 to date) and the red line gives the average for the last year.

This map shows symbols for the mean abundance at transect sites, with the colour of the symbol reflecting the level of abundance. Means are over all years. Grey background squares are the occupied cells as shown by the Butterflies for the New Millenium over the previous ten year period.

Coverage

In total, Wall has been recorded from 512 transects in the Butterfly Monitoring Scheme. Of these, annual indices of abundance have been calculated from 597 sites, with an average index of 11 individuals per site.

For 293 of these sites, Wall has been recorded well enough to calculate annual indices of abundance in more years, allowing trends to be calculated.

In 2017, 2530 individuals were recorded from 161 sites, producing annual indices at 118 of these.

This map shows the trend in abundance at particular transect sites for which data has been received within the last five years. Trends (increasing, declining or stable) are assessed at sites where the species has more than five years of annual index data. Use the option boxes below to view plots for individual sites.